Processing a substrate in a vacuum environment is a basic process in micro-fabrication technologies. A vacuum processing system 100 is shown in a perspective view in FIG. 1. The vacuum processing system 100 includes a vacuum chamber 110, a load lock or vacuum transfer chamber 120, and one or more processing chambers 130. The load lock 120 allows a work piece 140 (not shown in FIG. 1 for clarity reason) to be transferred between an ambient environment and the vacuum environment in the vacuum chamber 110. FIG. 2 shows a cross-sectional view of the vacuum processing system 100 of FIG. 1. FIG. 3 shows an enlarged view of the load lock 120 of the prior art vacuum processing system 100 in FIG. 1.
The work piece 140 can be transferred by a robot 115 from the vacuum chamber 110 to the processing chambers 130 wherein the work piece 140 can be processed in vacuum. The load lock 120 can include two or more gate valves 125, 126 that allow the load lock 120 to be isolated from or connected to the vacuum chamber 110 and the ambient environment. The work piece 140 can be transferred into the load lock through a first gate valve 125 while the load lock is sealed from the vacuum chamber 110 by the closing of the second gate valve 126. The first gate valve 125 is closed after the work piece 140 is transferred inside the load lock 120. The enclosure of the load lock 120 is pumped down to vacuum level. The second gate valve 126 can be then opened to allow the work piece to be transferred into the vacuum chamber 110. The vacuum chamber is subsequently pumped down to vacuum. The unloading of the work piece 140 can occur in a similar two-step process without exposing the vacuum chamber 110 or the processing chamber 130 to the ambient environment. The load lock 120 thus allows the process chamber 130 to maintain in a high-vacuum state during processing and during loading and unloading of work piece 140, which reduces contamination of the process chambers and avoid the extended pump-down of the process chamber.
Despite the above-described benefits, the load lock 120 is periodically exposed to atmosphere ambient environment and can cause indirect exposure of atmosphere ambient to the processing chamber 130 and the vacuum chamber 110. In many applications, such as physical vapor deposition (PVD), where very high vacuum is required, an additional or multiple transfer chambers need to be placed between the vacuum chamber 110 and load lock 120 to further reduce the base pressure in the vacuum chamber 110 and the contamination level of the processing chamber 130. One disadvantage of the vacuum processing system 100 is its large footprint due to horizontally extended multiple-chamber layout. The architecture of the vacuum processing system 100 would present a higher system cost and lower throughput in operation. Another disadvantage is it requires a complex robot mechanism to transfer work piece 140 between vacuum chamber 110 and transfer chamber and loadlock 120.